How Did Eratosthenes Estimate the Size of Earth in 240

Multiple Choice

How did Eratosthenes estimate the size of Earth in 240 B.C.?

A) by observing the duration of a solar eclipse
B) by measuring the size of Earth's shadow on the Moon in a lunar eclipse
C) by comparing the maximum altitude of the Sun in two cities at different latitudes
D) by sending fleets of ships around Earth
E) We don't know how he did it since all his writings were destroyed.